Common Pitfalls Using Astrogator's Target Sequence

There are several common cases where you may not get a successfully converged solution when using the differential corrector profile in a Target Sequence (also called the Targeter). This article provides approaches to mitigating or solving these common problems; most of these solutions are contained in a PDF file attached to the article.

Zero Eccentricity

One of the most common issues occurs when targeting zero eccentricity.

Problem

Eccentricity is a rough function because of the way it approaches zero from one side (it's impossible to have a negative eccentricity). This makes iterative methods messier and can sometimes lead to a non-convergent solution. The picture below demonstrates a case where a spacecraft is transferred from LEO to GEO but the Targeter has difficulty driving the eccentricity to zero within the specified tolerance.

Solution

To help drive the eccentricity to zero, flight-path angle is added as an additional constraint; because we know that a circular orbit will have a zero flight-path angle at every point along the orbit. Targeting both zero eccentricity and zero flight-path angle helps the Targeter converge more easily.

Further Reading

Some of the other common issues that users have experienced with the Targeter include targeting zero inclination, targeting zero eccentricity and zero inclination together, and converting impulsive burns to finite burns. These cases, as well as the case outlined above, are explained in more detail in the PDF file attached to this article.